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51317--9513-Monitoring Pitting Corrosion Growth in Steel Rebar Using Optical Fiber

An optical fiber corrosion sensor is developed to monitor the penetration of corrosion pits in steel bars. Simply made by encasing one end of an optical fiber into a steel straw. As corrosion penetrates the steel straw wall, the solution and corrosion products fill inside and contaminate the fiber end surface, resulting in a change in the reflectivity.

Product Number: 51317--9513-SG
ISBN: 9513 2017 CP
Author: Fujian Tang
Publication Date: 2017
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Use of optical fiber sensors to monitor steel corrosion has attracted a lot of interests in the past two decades due to its small size high precision and stability electromagnetic immunity possibility of being employed in large structures. In this study an optical fiber corrosion sensor is developed to monitor the growth of corrosion pits in steel bars in chloride-laden concrete environment. The sensor was simply made by encasing one end of an optical fiber into a steel straw. As the corrosion penetrates through the steel straw wall the corrosive solution and corrosion products fill in and contaminate the fiber end surface resulting in a change in the reflectivity. The change of the optical fiber reflectivity indicates the corrosion pits depth equaling to the straw wall thickness. Therefore by deploying corrosion sensors with different wall thicknesses in concrete structures the corrosion pit depth at different time periods can be monitored.The steel straw was fabricated from rebar steel with an inner diameter of 450 um and a total of four wall thicknesses were fabricated including 500 um 750 um 1000 um and 1250 um. The test solution was saturated Ca(OH)2 solution with sodium chloride and these corrosion sensors were immersed in the solution for one year. The change of reflectivity was recorded using an optical spectrum analyzer (OSA) weekly and the corrosion rate of the steel straw was measured with linear polarization resistance. After corrosion tests all the steel straws were taken out of the solution and the corrosion pits were observed using an optical microscopy. Finally a relationship between the change of the opical fiber reflectivity and the growth of the corrosion pits was established.

Key words: Corrosion, Pit depth, Reflectivity, EIS, LPR, Optical fiber

Use of optical fiber sensors to monitor steel corrosion has attracted a lot of interests in the past two decades due to its small size high precision and stability electromagnetic immunity possibility of being employed in large structures. In this study an optical fiber corrosion sensor is developed to monitor the growth of corrosion pits in steel bars in chloride-laden concrete environment. The sensor was simply made by encasing one end of an optical fiber into a steel straw. As the corrosion penetrates through the steel straw wall the corrosive solution and corrosion products fill in and contaminate the fiber end surface resulting in a change in the reflectivity. The change of the optical fiber reflectivity indicates the corrosion pits depth equaling to the straw wall thickness. Therefore by deploying corrosion sensors with different wall thicknesses in concrete structures the corrosion pit depth at different time periods can be monitored.The steel straw was fabricated from rebar steel with an inner diameter of 450 um and a total of four wall thicknesses were fabricated including 500 um 750 um 1000 um and 1250 um. The test solution was saturated Ca(OH)2 solution with sodium chloride and these corrosion sensors were immersed in the solution for one year. The change of reflectivity was recorded using an optical spectrum analyzer (OSA) weekly and the corrosion rate of the steel straw was measured with linear polarization resistance. After corrosion tests all the steel straws were taken out of the solution and the corrosion pits were observed using an optical microscopy. Finally a relationship between the change of the opical fiber reflectivity and the growth of the corrosion pits was established.

Key words: Corrosion, Pit depth, Reflectivity, EIS, LPR, Optical fiber

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